Method for transmitting control information and device therefor

ABSTRACT

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method for transmitting uplink control information and a device therefor, and the method comprises the steps of: selecting, from a plurality of uplink control channel resources, one uplink control channel resource corresponding to a plurality of HARQ-ACKs; and transmitting bit values corresponding to said plurality of HARQ-ACKs by using the selected uplink control channel resource.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting control information andan apparatus therefore.

BACKGROUND ART

Wireless communication systems are widely developed to provide variouscommunication services such as voice or data services. In general,wireless communication systems are multiple access systems capable ofsharing available system resources (bandwidths, transmission power,etc.) to support communication with multiple users. Examples of multipleaccess systems include Code Division Multiple Access (CDMA), FrequencyDivision Multiple Access (FDMA), Time Division Multiple Access (TDMA),OFDMA (Orthogonal Frequency Division Multiple Access), SC-FDMA (SingleCarrier Frequency Division Multiple Access), etc.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for efficiently transmitting uplink control information and anapparatus therefore.

Another object of the present invention devised to solve the problemlies in a method for efficiently transmitting control information,preferably, ACK/NACK information in a multi-carrier environment and anapparatus therefore.

It will be appreciated by persons skilled in the art that the objectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and the above and otherobjects that the present invention can achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The objects of the present invention can be achieved by providing amethod for transmitting uplink control information in a situation inwhich a plurality of cells including a primary cell and a secondary cellis configured in a wireless communication system, the method comprising:selecting one PUCCH resource corresponding to a plurality of HARQ-ACKs(Hybrid Automatic Repeat reQuest-Acknowledgements) from a plurality ofPUCCH resources for PUCCH (Physical Uplink Control Channel) format 1;and transmitting bit values corresponding to the plurality of HARQ-ACKsusing the selected PUCCH resource, wherein the relationship among theplurality of HARQ-ACKs, PUCCH resource and bit values includes therelationship of Table 1

TABLE 1 HARQ- HARQ- ACK(0) ACK(1) n⁽¹⁾ _(PUCCH,i) b(0)b(1) ACK NACK/DTXn⁽¹⁾ _(PUCCH,0) 11 NACK NACK/DTX n⁽¹⁾ _(PUCCH,0) 00where HARQ-ACK(0) indicates ACK/NACK/DTX response to a data blockrelated to the primary cell, HARQ-ACK(1) indicates ACK/NACK/DTX responseto a data block related to the secondary cell, n⁽¹⁾ _(PUCCH, i) (i=0, 1)indicates a plurality of PUCCH resources for the PUCCH format 1, n⁽¹⁾_(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH (PhysicalDownlink Control Channel) on the primary cell, and b(0)b(1) indicatesthe bit values.

The objects of the present invention can be achieved by providing acommunication apparatus configured to transmit uplink controlinformation in a situation in which a plurality of cells including aprimary cell and a secondary cell is configured in a wirelesscommunication system, the communication apparatus comprising a radiofrequency (RF) unit and a processor, wherein the processor is configuredto select one PUCCH resource corresponding to a plurality of HARQ-ACKs(Hybrid Automatic Repeat reQuest-Acknowledgements) from a plurality ofPUCCH resources for PUCCH (Physical Uplink Control Channel) format 1 andtransmit bit values corresponding to the plurality of HARQ-ACKs usingthe selected PUCCH resource, wherein the relationship among theplurality of HARQ-ACKs, PUCCH resource and bit values includes therelationship of the following Table 1

TABLE 1 HARQ- HARQ- ACK(0) ACK(1) n⁽¹⁾ _(PUCCH,i) b(0)b(1) ACK NACK/DTXn⁽¹⁾ _(PUCCH,0) 11 NACK NACK/DTX n⁽¹⁾ _(PUCCH,0) 00where HARQ-ACK(0) indicates ACK/NACK/DTX response to a data blockrelated to the primary cell, HARQ-ACK(1) indicates ACK/NACK/DTX responseto a data block related to the secondary cell, n⁽¹⁾ _(PUCCH, i) (i=0, 1)indicates a plurality of PUCCH resources for the PUCCH format 1, n⁽¹⁾_(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH (PhysicalDownlink Control Channel) on the primary cell, and b(0)b(1) indicatesthe bit values.

The relationship among the plurality of HARQ-ACKs, PUCCH resource andbit values may further include the relationship of the following Table 2

TABLE 2 HARQ- HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2) ACK(3) n⁽¹⁾_(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACKNACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX NACK/DTXn⁽¹⁾ _(PUCCH, 0) 01 NACK NACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00where HARQ-ACK(0)(1) indicates ACK/NACK/DTX responses to data blocksrelated to the primary cell, HARQ-ACK(2)(3) indicates ACK/NACK/DTXresponses to data blocks related to the secondary cell, n⁽¹⁾ _(PUCCH, i)(i=0, 1, 2, 3) indicates a plurality of PUCCH resources for the PUCCHformat 1, n⁽¹⁾ _(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH(Physical Downlink Control Channel) on the primary cell, and b(0)b(1)indicates the bit values.

n⁽¹⁾ _(PUCCH, 0) may include PUCCH resources for PUCCH format 1,desirably, PUCCH format 1b.

The relationship of Table 1 may further include a case in whichtransmission of the plurality of HARQ-ACKs is dropped if HARQ-ACK(0) isDTX and HARQ-ACK(1) is NACK.

The relationship of Table 2 may further include a case in whichtransmission of the plurality of HARQ-ACKs is dropped if HARQ-ACK(0) andHARQ-ACK(1) are DTX and HARQ-ACK(2) and HARQ-ACK(3) are NACK.

The primary cell may include a primary component carrier (PCC) and thesecondary cell may include a secondary component carrier (SCC).

The uplink control channel may include a PUCCH (Physical Uplink ControlChannel) and the downlink control channel may include a PDCCH (PhysicalDownlink Control Channel).

The objects of the present invention can be achieved by providing amethod for transmitting uplink control information in a situation inwhich a plurality of cells including a primary cell and a secondary cellis configured in a wireless communication system, the method comprising:selecting one uplink control channel resource corresponding to aplurality of HARQ-ACKs from a plurality of uplink control channelresources; and transmitting modulation symbols corresponding to theplurality of HARQ-ACKs using the selected uplink control channelresource, wherein a mapping relationship between the plurality ofHARQ-ACKs and the modulation symbols is equal to a mapping result ofHARQ-ACKs and modulation symbols for one or more data blocks received ona single downlink carrier on the basis of one or more first HARQ-ACKsfor one or more data blocks related to the primary cell, if one or moresecond HARQ-ACKs for one or more data blocks related to the secondarycell, except the one or more first HARQ-ACKs, are all NACK or DTX(Discontinuous Transmission).

The objects of the present invention can be achieved by providing acommunication apparatus configured to transmit uplink controlinformation in a situation in which a plurality of cells including aprimary cell and a secondary cell is configured in a wirelesscommunication system, the communication apparatus comprising an RF(Radio Frequency) unit and a processor, wherein the processor isconfigured to select one uplink control channel resource correspondingto a plurality of HARQ-ACKs from a plurality of uplink control channelresources, and transmit modulation symbols corresponding to theplurality of HARQ-ACKs using the selected uplink control channelresource, wherein a mapping relationship between the plurality ofHARQ-ACKs and the modulation symbols is equal to a mapping result ofHARQ-ACKs and modulation symbols for one or more data blocks received ona single downlink carrier on the basis of one or more first HARQ-ACKsfor one or more data blocks related to the primary cell, if one or moresecond HARQ-ACKs for one or more data block related to the secondarycell, except the one or more first HARQ-ACKs, are all NACK or DTX(Discontinuous Transmission).

The transmission of the plurality of HARQ-ACKs may be dropped if the oneor more first HARQ-ACKs are all DTX and the second HARQ-ACKs are allNACK.

The primary cell may include a PCC (Primary Component Carrier) and thesecondary cell may include a SCC (Secondary Component Carrier).

The uplink control channel may include a PUCCH (Physical Uplink ControlChannel) and the downlink control channel may include a PDCCH (PhysicalDownlink Control Channel).

Advantageous Effects

According to the present invention, uplink control information can beefficiently transmitted in a wireless communication system. Furthermore,control information, preferably, ACK/NACK information can be efficientlytransmitted in a multi-carrier environment.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 shows an exemplary radio frame structure;

FIG. 2 shows a resource grid of a downlink slot;

FIG. 3 shows a downlink subframe structure;

FIG. 4 shows an uplink subframe structure;

FIG. 5 shows an example of physically mapping PUCCH formats to PUCCHregions;

FIG. 6 shows a slot level structure of PUCCH format 2/2a/2b;

FIG. 7 shows a slot level structure of PUCCH format 1a/1b;

FIG. 8 shows an example of determining PUCCH resources for ACK/NACK;

FIG. 9 shows a carrier aggregation communication system;

FIG. 10 shows scheduling in the case of aggregation of multiplecarriers;

FIG. 11 shows operations of a base station and a user equipment in a DLCC change period;

FIG. 12 shows a PUCCH format 1a/1b based ACK/NACK selection methodaccording to LTE;

FIGS. 13 to 24 show methods of transmitting ACK/NACK according toembodiments of the present invention; and

FIG. 25 shows a base station and a UE applicable to an embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Techniques described herein can be used in various wireless accesssystems such as CDMA, FDMA, TDMA, OFDMA, SC-FDMA, etc. CDMA may beimplemented with a radio technology such as Universal Terrestrial RadioAccess (UTRA) or CDMA2000. TDMA may be implemented with a radiotechnology such as Global System for Mobile communication (GSM)/GeneralPacket Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution(EDGE). OFDMA may be implemented with a radio technology such asinstitute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi),IEEE 802.16 (WiMAX), IEEE 802-20, evolved-UTRA (E-UTRA) etc. The UTRA isa part of a universal mobile telecommunication system (UMTS). 3^(rd)generation partnership project (3GPP) long term evolution (LTE) is apart of an evolved-UMTS (E-UMTS) using the E-URTA. The 3GPP LTE employsthe OFDMA in downlink and employs the SC-FDMA in uplink. LTE-advanced(LTE-A) is an evolution of 3GPP LTE.

For clarity, this application focuses on 3GPP LTE/LTE-A. However,technical features of the present invention are not limited thereto.Furthermore, specific terminology used in the following description isprovided to help understand the present invention and may be changed toother forms within the technical spirit of the present invention.

FIG. 1 shows a structure of a radio frame.

Referring to FIG. 1, a radio frame includes 10 subframes. A subframeincludes two slots in the time domain. A time for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may have a length of 1 millisecond (ms), and one slot mayhave a length of 0.5 ms. One slot includes a plurality of orthogonalfrequency division multiplexing (OFDM) or single carrier frequencydivision multiple access (SC-FDMA) symbols in the time domain. Since theLET uses OFDMA in the downlink and uses SC-FDMA in the uplink, the OFDMor SC-FDMA symbol represents one symbol period. A resource block (RB) isa resource allocation unit and includes a plurality of contiguoussubcarriers in one slot. The structure of the radio frame is shown forexemplary purposes only. Thus, the number of subframes included in theradio frame or the number of slots included in the subframe or thenumber of symbols included in the slot may be modified in variousmanners.

FIG. 2 shows a resource grid for a downlink slot.

Referring to FIG. 2, a downlink slot includes a plurality of OFDMsymbols in the time domain. It is described herein that one downlinkslot may include 7(6) OFDM symbols, and one RB may include 12subcarriers in frequency domain as an example. Each element on theresource grid is referred to as a resource element (RE). One RB includes12×7(6) REs. The number NRB of RBs included in the downlink slot dependson downlink transmit bandwidth. Though the structure of an uplink slotmay be same as that of the downlink slot, OFDM symbols are replaced withSC-FDMA symbols.

FIG. 3 shows a structure of a downlink subframe.

Referring to FIG. 3, a maximum of three (four) OFDM symbols located in afront portion of a first slot within a subframe correspond to a controlregion to be assigned with a control channel. The remaining OFDM symbolscorrespond to a data region to be assigned with a physical downlinkshared channel (PDSCH). The PDSCH is used to carry a transport block(TB) or a codeword (CW) corresponding to the transport block. The TBmeans a data block transmitted from a MAC layer to a PHY layer through atransmission channel. The CW corresponds to a coded version of the TB.The relationship between the TB and CW may depend on swapping. In thespecification, PDSCH, transport block and codeword are used in a mixedmanner. Examples of downlink control channels used in the LTE include aphysical control format indicator channel (PCFICH), a physical downlinkcontrol channel (PDCCH), a physical hybrid ARQ indicator channel(PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of asubframe and carries information regarding the number of OFDM symbolsused for transmission of control channels within the subframe. The PHICHis a response of uplink transmission and carries a HARQ acknowledgement(ACK)/not-acknowledgement (NACH) signal.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI includes resource allocationinformation and other control information for a user equipment (UE) orUE group. For example, the DCI includes uplink/downlink schedulinginformation, an uplink transmit (Tx) power control command, etc.Information regarding transmission modes and DCI formats forconstructing a multi-antenna technique are as follows.

Transmission Mode

-   -   Transmission mode 1: Transmission from a single base station        antenna port    -   Transmission mode 2: Transmit diversity    -   Transmission mode 3: Open-loop spatial multiplexing    -   Transmission mode 4: Closed-loop spatial multiplexing    -   Transmission mode 5: Multi-user MIMO    -   Transmission mode 6: Closed-loop rank-1 precoding    -   Transmission mode 7: Transmission using UE-specific reference        signals

DCI Formats

-   -   Format 0: Resource grants for PUSCH transmission (uplink)    -   Format 1: Resource assignments for single codeword PDSCH        transmission (transmission modes 1, 2 and 7)    -   Format 1A: Compact signaling of resource assignments for single        codeword PDSCH (all modes)    -   Format 1B: Compact resource assignments for PDSCH using rank-1        closed loop precoding (mode 6)    -   Format 1C: Very compact resource assignments for PDSCH (e.g.        paging/broadcast system information)    -   Format 1D: Compact resource assignments for PDSCH using        multi-user MIMO (mode 5)    -   Format 2: Resource assignments for PDSCH for closed-loop MIMO        operation (mode 4)    -   Format 2A: Resource assignments for PDSCH for open-loop MIMO        operation (mode 3)    -   Format 3/3A: Power control commands for PUCCH and PUSCH with        2-bit/1-bit power adjustment

As described above, the PDSCH may carry a transport format and resourceallocation information of a downlink shared channel (DL-SCH), atransport format and resource allocation information of an uplink sharedchannel (UL-SCH), paging information on a paging channel (PCH), systeminformation on the DL-SCH, resource allocation information of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region. A UE can monitor the plurality of PDCCHs. ThePDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups(REGs). A format of the PDCCH and the number of bits of the PDCCH aredetermined according to the number of CCEs. A base station (BS)determines PDCCH format according to a DCI to be transmitted to the UE,and attaches a cyclic redundancy check (CRC) to control information. TheCRC is masked with an identifier (referred to as a radio networktemporary identifier (RNTI)) according to an owner or usage of thePDCCH. If the PDCCH is for a specific UE, for example, an identifier(e.g., cell-RNTI)) of the UE may be masked to the CRC. Alternatively, ifthe PDCCH is for a paging message, a paging identifier (e.g.,paging-RNTI (P-RNTI)) may be masked to the CRC. If the PDCCH is forsystem information (more specifically, a system information block(SIB)), system information RNTI (SI-RNTI) may be masked to the CRC. Ifthe PDCCH is for a random access response, random access-RNTI (RA-RNTI)may be masked to the CRC.

FIG. 4 shows a structure of an uplink subframe used in LTE.

Referring to FIG. 4, the uplink subframe includes a plurality of slots(for example, two slots). A slot may includes a number of SC-FDMAsymbols depending on CP length. The uplink subframe is divided in afrequency domain into a control region and a data region. The dataregion includes a PUSCH and is used to transmit a data signal such as avoice signal, etc. The control region includes a PUCCH and is used totransmit uplink control information (UCI). The PUCCH includes an RB pairlocated at both ends of the data region in the frequency domain and hopsbased on the slots.

The PUCCH can be used to transmit the following control information.

-   -   Scheduling Request (SR): Information used to request uplink        UL-SCH resources, which is transmitted using on-off keying        (OOK).    -   HARQ ACK/NACK: A response to downlink data packets on PDSCH,        which indicates whether the downlink data packets have been        successfully received. One ACK/NACK bit is transmitted in        response to a single downlink codeword and two ACK/NACK bits are        transmitted in response to two downlink codewords.    -   Channel Quality Indicator (CQI): Feedback information regarding        a downlink channel. MIMO-related feedback information includes a        rank indicator (RI) and a precoding matrix indicator (PMI). 20        bits are used for each subframe.

The amount of control information which a UE can transmit in a subframedepends on the number of SC-FDMA symbols available for transmission ofcontrol information. The SC-FDMA symbols available for transmission ofcontrol information correspond to SC-FDMA symbols excluding SC-FDMAsymbols used for reference signal transmission in a subframe. In thecase of a subframe for which a sounding reference signal (SRS) is set,even the last SC-FDMA symbol of the subframe is excluded. The referencesignal is used to detect coherency of the PUCCH. The PUCCH supportsseven different formats depending on the information to be signaled.

Table 1 shows the mapping between the PUCCH format and UCI supported inthe LTE.

TABLE 1 PUCCH format Uplink Control Information (UCI) Format 1Scheduling Request (SR) (unmodulated waveform) Format 1a 1-bit HARQACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACK with/without SRFormat 2 CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK(20 bits) for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK(20 + 1 coded bits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 codedbits)

FIG. 5 shows an example of physical mapping of PUCCH formats to PUCCHregions.

Referring to FIG. 5, PUCCH CQI formats 2/2a/2b are mapped andtransmitted on the band-edge RBs (e.g. PUCCH region m=0, 1) followed bya mixed PUCCH RB (if present, e.g. region m=2) of CQI format 2/2a/2b andSR/HARQ ACK/NACK format 1/1a/1b, and then by PUCCH SR/HARQ ACK/NACKformat 1/1a/1b (e.g. m=3, 4, 5). The number of PUCCH RBs available foruse by PUCCH CQI format 2/2a/2b is indicated to the UEs in the cell bybroadcast signaling.

The periodicity and frequency resolution to be used by a UE to reportCQI are both controlled by the BS. In the time domain, both periodic andaperiodic CQI reporting are supported. The PUCCH format 2 is used forperiodic CQI reporting only. However, if a PUSCH is scheduled for asubframe supposed to transmit a CQI, the CQI is fed back to data andthen transmitted through the PUSCH. The PUSCH is used for aperiodicreporting of the CQI. For this, the BS instructs the UE to send anindividual CQI report embedded into a resource (that is, PUSCH) which isscheduled for uplink data transmission.

FIG. 6 shows a slot level structure of PUCCH format 2/2a/2b. The PUCCHformat 2/2a/2b is used for CQI transmission. SC-FDMA symbols 1 and 5 areused for demodulation reference signal (DM RS) transmission in a slot inthe case of normal cyclic prefix (CP). In the case of extended CP, onlySC-FDMA symbol 3 is used for DM RS transmission in the slot.

Referring to FIG. 6, 10 CQI information bits are channel coded with arate ½ punctured (20, k) Reed-Muller code to give 20 coded bits (notshown), which are then scrambled (not shown) prior to quadrature phaseshift keying (QPSK) constellation mapping. The coded bits may bescrambled in a similar way to PUSCH data with a length-31 Gold sequence.10 QPSK modulated symbols are generated and 5 QPSK modulated symbols d0to d4 are transmitted in each slot through corresponding SC-FDMAsymbols. Each QPSK modulated symbol is used to modulate a base RSsequence (ru, 0) of length-12 prior to Inverse Fast Fourier Transform(IFFT). Consequently, the RS sequences are cyclic shifted(d_(x)*r_(u,0), x=0 to 4) according to QPSK modulated symbol values inthe time domain. The RS sequences multiplied by the QPSK modulatedsymbol values are cyclic shifted (α_(cs,x), x=1, 5). When the number ofcyclic shifts is N, N UEs can be multiplexed on the same CQI PUCCH RB.The DM RS sequence is similar to the frequency domain CQI sequence butwithout the CQI data modulation.

Parameters/resources for periodic CQI reporting are semi-staticallyconfigured by higher layer signaling. For example, if PUCCH resourceindex n⁽²⁾ _(PUCCH) is set for CQI transmission, the CQI is periodicallytransmitted on the CQI PUCCH linked to the PUCCH resource index n⁽²⁾_(PUCCH). The PUCCH resource index n⁽²⁾ _(PUCCH) indicates the PUCCH RBand cyclic shift α_(cs).

FIG. 7 shows a slot level structure of PUCCH format 1a/1b. The PUCCHformat 1a/1b is used for ACK/NACK transmission. SC-FDMA symbols 2, 3 and4 are used for DM RS transmissions in the case of normal CP. In the caseof extended CP, SC-FDMA symbol 2 and 3 are used for DM RS transmission.Accordingly, four SC-FDMA symbols are used for ACK/NACK transmission inone slot. The PUCCH format 1a/1b is referred to as PUCCH format 1 forconvenience.

Referring to FIG. 7, one ACK/NACK information bit [b(o)] and twoACK/NACK information bits [(b0)b(1)] are modulated using BPSK and QPSKmodulation respectively, resulting in a single HARQ ACK/NACK modulationsymbol. Each bit [b(i), i=0, 1] in the ACK/NACK information represents aHARQ response to a corresponding DL transmission block. A positive ACKis encoded as a binary ‘1’ and a negative ACK (NACK) as a binary ‘0’.Table 2 shows a modulation table defined for the PUCCH formats 1a and 1bin LTE.

TABLE 2 PUCCH format b(0), . . . , b(M_(bit) − 1) d(0) 1a 0  1 1 −1 1b00  1 01 −j 10  j 11 −1

In addition to the cyclic time shift (α_(cs,x)) in the frequency domainas in the CQI case above, the PUCCH formats 1a/1b perform time domainspreading using orthogonal (Walsh-Hadamard or DFT) spreading codes w0,w1, w2 and w3. Since code multiplexing is used in both the frequency andtime domains in the case of PUCCH format 1a/1b, a large number of UEscan be multiplexed on the same PUCCH RB.

RSs transmitted from different UEs are multiplexed in the same way asUCI. The number of cyclic shifts supported in an SC-FDMA symbol forPUCCH ACK/NACK RBs is configurable by a cell-specific higher-layersignaling parameter Δ^(PUCCH) _(shift)ε{1, 2, 3}, indicating 12, 6, or 4shifts respectively. For the time-domain CDM, the number of spreadingcodes for ACK/NACK data is limited by the number of RS symbols, as themultiplexing capacity of RS symbols is smaller than that of USI symbolsdue to smaller number of RS symbols.

FIG. 8 shows an example of determining PUCCH resources for ACK/NACKinformation. A PUCCH resource for ACK/NACK information is not allocatedto each UE in the cell in advance in the LTE system, and a plurality ofUEs in the cell share a plurality of PUCCH resources at each point oftime. Specifically, a PUCCH resource that a UE uses to transmit theACK/NACK information corresponds to a PDCCH that carries schedulinginformation regarding corresponding downlink data. A region in which thePDCCH is transmitted in each downlink subframe is configured with aplurality of control channel elements (CCEs), and the PDCCH transmittedto the UE is configured with one or more CCEs. The UE transmits theACK/NACK information through the PUCCH resource corresponding to aspecific CCE (e.g. first CCE) among the CCEs constructing the PDCCHreceived by the UE.

Referring to FIG. 8, blocks in a downlink component carrier (DL CC)indicate CCEs and blocks in an uplink component carrier (UL CC) indicatePUCCH resources. Each PUCCH index corresponds to a PUCCH resource forACK/NACK information. If information about a PDSCH is transmittedthrough the PDCCH consisting of CCEs 4, 5 and 6, as shown in FIG. 8, theUE transmits the ACK/NACK information through the PUCCH 4 correspondingto the CCE 4 that is the first CCE. FIG. 8 shows an exemplary case inwhich the UL CC has a maximum of M PUCCHs when the DL CC has a maximumof N CCEs. Although N may equal M, it can be possible to design thesystem such that M is different from N and to overlap mappings of theCCEs and PUCCHs.

Specifically, the PUCCH resource index in the LTE system is determinedas follows.

n ⁽¹⁾ _(PUCCH) =n _(CCE) +N ⁽¹⁾ _(PUCCH)  [Equation 1]

Here, n⁽¹⁾ _(PUCCH) represents a resource index of the PUCCH format 1for ACK/NACK/DTX transmission, N⁽¹⁾ _(PUCCH) represents a signalingvalue transmitted from a higher layer, and n_(CCE) represents the lowestvalue among CCE indexes used for PDCCH transmission. Cyclic shifts,orthogonal spreading codes and physical resource block (PRE) for thePUCCH format 1a/1b are derived from the n⁽¹⁾ _(PUCCH).

When the LTE system operates in TDD, the UE transmits one multiplexedACK/NACK signal for a plurality of PDSCHs received through subframes atdifferent time points. Specifically, the UE transmits one multiplexedACK/NACK signal for a plurality of PDSCHs using PUCCH selection. In thePUCCH selection, the UE occupies a plurality of uplink physical channelsto transmit the multiplexed ACK/NACK signal when receiving a pluralityof downlink data signals. When the UE receives a plurality of PDSCHs,for example, the UE can occupy the same number of PUCCHs as the numberof the PDSCHs using specific CCEs of the PUCCHs, which indicate thePDSCHs. In this case, the UE can transmit the multiplexed ACK/NACKsignal using a combination of information on which one of the occupiedPUCCHs is selected and modulated/coded information applied to theselected PUCCH.

Table 3 shows a PUCCH selection method defined in the LTE system.

TABLE 3 Subframe ACK(0), ACK(1), ACK(2), ACK(3) n⁽¹⁾ _(PUCCH,X) b(0),b(1) ACK, ACK, ACK, ACK n⁽¹⁾ _(PUCCH,1) 1, 1 ACK, ACK, ACK, NACK/DTXn⁽¹⁾ _(PUCCH,1) 1, 0 NACK/DTX, NACK/DTX, NACK, DTX n⁽¹⁾ _(PUCCH,2) 1, 1ACK, ACK, NACK/DTX, ACK n⁽¹⁾ _(PUCCH,1) 1, 0 NACK, DTX, DTX, DTX n⁽¹⁾_(PUCCH,0) 1, 0 ACK, ACK, NACK/DTX, NACK/DTX n⁽¹⁾ _(PUCCH,1) 1, 0 ACK,NACK/DTX, ACK, ACK n⁽¹⁾ _(PUCCH,3) 0, 1 NACK/DTX, NACK/DTX, NACK/DTX,n⁽¹⁾ _(PUCCH,3) 1, 1 NACK ACK, NACK/DTX, ACK, NACK/DTX n⁽¹⁾ _(PUCCH,2)0, 1 ACK, NACK/DTX, NACK/DTX, ACK n⁽¹⁾ _(PUCCH,0) 0, 1 ACK, NACK/DTX,NACK/DTX, NACK/DTX n⁽¹⁾ _(PUCCH,0) 1, 1 NACK/DTX, ACK, ACK, ACK n⁽¹⁾_(PUCCH,3) 0, 1 NACK/DTX, NACK, DTX, DTX n⁽¹⁾ _(PUCCH,1) 0, 0 NACK/DTX,ACK, ACK, NACK/DTX n⁽¹⁾ _(PUCCH,2) 1, 0 NACK/DTX, ACK, NACK/DTX, ACKn⁽¹⁾ _(PUCCH,3) 1, 0 NACK/DTX, ACK, NACK/DTX, NACK/DTX n⁽¹⁾ _(PUCCH,1)0, 1 NACK/DTX, NACK/DTX, ACK, ACK n⁽¹⁾ _(PUCCH,3) 0, 1 NACK/DTX,NACK/DTX, ACK, NACK/DTX n⁽¹⁾ _(PUCCH,2) 0, 0 NACK/DTX, NACK/DTX,NACK/DTX, ACK n⁽¹⁾ _(PUCCH,3) 0, 0 DTX, DTX, DTX, DTX N/A N/A

In Table 3, ACK(i) indicates the HARQ ACK/NACK/DTX result for an i-thdata unit (0≦i≦3). Discontinuous transmission (DTX) means that there isno data unit transmitted for corresponding ACK(i) or the UE does notdetect the existence of the data unit corresponding to HARQ-ACK(i). TheUE can occupy a maximum of four PUCCH resources (i.e., n⁽¹⁾ _(PUCCH,0)to n⁽¹⁾ _(PUCCH,3)) for each data unit. The multiplexed ACK/NACK signalis transmitted through one PUCCH resource selected from among theoccupied PUCCH resources. In Table 3, n⁽¹⁾ _(PUCCH,X) indicates thePUCCH resource which should be used in actual ACK/NACK transmission, andb(0)b(1) indicates two bits carried by the selected PUCCH resource,which is modulated using QPSK. If the UE decodes four data unitssuccessfully, the UE should transmit two bits (1, 1) to the BS usingPUCCH resource n⁽¹⁾ _(PUCCH,1). Since combinations of PUCCH resourcesand QPSK symbols cannot represent all of available ACK/NACK, NACK andDTX are coupled (NACK/DTX, N/D) except in some cases.

FIG. 9 shows a carrier aggregation (CA) communication system. The LTE-Asystem uses carrier aggregation or bandwidth aggregation that uses awider uplink/downlink bandwidth by aggregating a plurality ofuplink/downlink frequency blocks for a wider frequency band. Eachfrequency block is transmitted using a component carrier (CC). Thecomponent carrier may be understood as a carrier frequency (or centercarrier, center frequency) for the corresponding frequency block.

Referring to FIG. 9, a wider uplink/downlink bandwidth can be supportedby aggregating a plurality of uplink/downlink CCs. The CCs may becontiguous or noncontiguous in the frequency domain. The bandwidths ofthe CCs can be independently determined. Asymmetrical carrieraggregation in which the number of UL CCs differs from the number of DLCCs may be used. In the case of two DL CCs and one UL CC, for example,they may be configured such that the DL CCs and UL CC correspond to eachother 2:1. The DL CC/UL CC link may be fixed to the system orsemi-statically configured. Furthermore, even if the entire systembandwidth is configured with N CCs, a frequency band that a specific UEcan monitor/receive may be limited to M (<N) CCs. Various parametersregarding carrier aggregation may be set cell-specifically, UEgroup-specifically, or UE-specifically. Meanwhile, control informationmay be configured such that the control information can be transmittedand received only through a specific CC. This specific CC may bedesignated as a primary CC (PCC) (or anchor CC) and other CCs may bedesignated as secondary CC (SCCs).

LTE-A uses the concept of cells to manage radio resources. The cell isdefined as a combination of downlink and uplink resources. Here, theuplink resource is not an essential component. Accordingly, the cell canbe configured with the downlink resource alone, or with both thedownlink resource and uplink resource. When carrier aggregation issupported, linkage between a downlink resource carrier frequency (or DLCC) and an uplink resource carrier frequency (or UL CC) may bedesignated by system information. A cell that operates on the primaryfrequency (or PCC) may be designated as a primary cell (Pcell) and acell that operates on the secondary frequency (or SCC) is designated asa secondary cell (SCell). The PCell is used for the UE to performinitial connection establishment or connection re-establishment. PCellmay represent a cell designated during a handover process. The SCell isconfigurable after RRC connection establishment and may be used toprovide additional radio resources. The PCell and SCell may be commonlydesignated as a serving cell. Accordingly, for a UE that is in anRRC_CONNECTED state without carrier aggregation or does not supportcarrier aggregation, only one serving cell configured with only thePCell exists. On the other hand, for a UE in an RRC_CONNECTED state, forwhich carrier aggregation is set, one or more serving cells includingthe PCell and SCell exist. For carrier aggregation, a network mayconfigure one or more SCells for a UE that supports carrier aggregationin addition to the PCell initially configured in the connectionestablishment process after initial security activation.

FIG. 10 illustrates scheduling when a plurality of carriers isaggregated. It is assumed that three DL CCs are aggregated and DL CC Ais set to PDCCH CC. DL CCs A, B and C may be designated as serving CCs,serving carriers, and serving cells. When a CIF is disabled, each DL CCcan transmit only the PDCCH scheduling its own PDSCH without the CIF, byfollowing the LTE PDCCH principle. On the other hand, if the CIF isenabled by UE-specific (or UE-group-specific or cell-specific) higherlayer signaling, the DL CC A (PDCCH CC) can transmit the PDCCHsscheduling not only its own PDSCH but also PDSCHs of the other CCs, byusing the CIF. In this case, no PDCCH is transmitted on the DL CCs B andC which are not configured as the PDCCH CCs. Accordingly, the DL CC A(PDCCH CC) must include all of a PDCCH search space related to the DL CCA, a PDCCH search space related to the DL CC B and a PDCCH search spacerelated to the DL CC C.

The LTE-A considers feedback of a plurality of ACK/NACKinformation/signals with respect to a plurality of PDSCHs transmittedthrough a plurality of DL CCs, through a specific UL CC (e.g. UL PCC orUL PCell). If the UE operates in Single User Multiple Input MultipleOutput (SU-MIMO) in a certain DL CC to receive two codewords (ortransmission blocks), the UE needs to transmit a total of four feedbackstates of ACK/ACK, ACK/NACK, NACK/ACK, and NACK/NACK, or a maximum offive feedback states including DTX for the DL CC. If the DL CC isconfigured such that the DL CC supports a single codeword (ortransmission block), a maximum of three states of ACK, NACK, and DTXexist for the DL CC. If NACK is processed in the same manner as DTX, atotal of two feedback states of ACK and NACK/DTX exist for the DL CC.Accordingly, if the UE aggregates a maximum of five DL CCs and operatesin the SU-MIMO mode in all the CCs, the UE can have a maximum of 5⁵transmittable feedback states, and an ACK/NACK payload size forrepresenting the feedback states becomes 12 bits. If DTX is processed inthe same manner as NACK, the number of feedback states becomes 4⁵ and anACK/NACK payload size for representing the 4⁵ feedback states becomes 10bits.

For this, it is discussed that a plurality of ACK/NACK informationsignals are channel coded (for example, Reed-Muller coded, Tail-bitingconvolutional coded, etc.), and then transmitted using the PUCCH format2, or a new PUCCH format (for example, block-spreading based PUCCHformat) in the LTE-A. Furthermore, it is discussed that a plurality ofACK/NACK information/signals are transmitted using the PUCCH format1a/1b and ACK/NACK multiplexing (i.e., ACK/NACK selection) in the LTE-A.

The LTE TDD system uses implicit ACK/NACK selection that uses PDCCHresources (linked to a lowest CCE index) respectively corresponding toPDSCHs scheduling PDSCHs to secure PUCCH resources as an ACK/NACKmultiplexing (i.e., ACK/NACK selection) method. However, if the implicitACK/NACK selection is applied using PUCCH resources in different RBs,performance deterioration may occur. Accordingly, the LTE-A considersexplicit ACK/NACK selection that uses reserved PUCCH resources,preferably, a plurality of PUCCH resources in the same RB or contiguousRBs, for each UE through RRC signaling.

However, when ACK/NACK information with respect to a plurality of CCs istransmitted using the explicit ACK/NACK selection, a plurality ofexplicitly reserved resources is used for ACK/NACK transmission althoughone CC is actually scheduled by the BS. For example, when only one DL CC(i.e., primary/anchor DL CC) linked to an ACK/NACK transmit UL CC amonga plurality of DL CCs is scheduled, explicit PUCCH resources may beunnecessarily used even though implicitly designated (i.e., linked tothe lowest CCE index transmitting PDCCH) PUCCH resources (i.e., PUCCHformat 1a/1b) are available. More comprehensively, even if one or moreCCs including the primary/anchor DL CC are simultaneously scheduled, asituation in which NACK or DTX is transmitted for CCs other than theprimary/anchor DL CC may be generated. In this case, explicit PUCCHresources are also unnecessarily used.

The LTE-A can reconfigure carrier configuration, and thus ACK/NACKinformation inconsistency between the UE and BS may be generated. FIG.10 illustrates operations of the BS and UE in a DL CC reconfigurationperiod.

Referring to FIG. 11, when the BS reconfigures DL CC(s) that the UE canuse by RRC reconfiguration or L1/L2 control signaling, timings ofapplying the reconfigured DL CC(s) to the BS and UE may differs fromeach other. For example, if the BS changes the number of CCs that the UEcan use from three to two, the time when the BS changes the number of DLCCs from three to two and transmits downlink data may be different fromthe time when the UE changes the number of serving DL CCs from three totwo. Furthermore, even though the BS instructs the UE to change thenumber of CCs, a time period in which the number of DL CCs that the UEknows is different from the number of DL CCs that the BS knows may begenerated if the UE fails to receive the instruction from the BS.

Accordingly, the UE may transmit ACK/NACK information for three DL CCsto the BS although the BS expects ACK/NACK information for two DL CCs.On the contrary, the UE may transmit ACK/NACK information for two DL CCsto the BS though the BS expects ACK/NACK information for three DL CCs.When the UE transmits the ACK/NACK information for three DL CCs whilethe BS recognizes that the number of DL CCs is two, the BS attempts todemodulate the ACK/NACK information received from UE on the basis of theACK/NACK information for two DL CCs. In this case, the ACK/NACKinformation cannot be correctly demodulated. That is, ACK/NACKinformation inconsistency between the BS and UE may be generated due toconfusion of DL CC configuration.

A method for efficiently transmitting uplink control information,preferably ACK/NACK information when carriers (carriers, frequencyresources, cells, etc.) are aggregated and a resource allocation methodtherefore will now be explained with reference to the attached drawings.For convenience of explanation, it is assumed that two CCs areconfigured for one UE in the following description. In addition, it isassumed that a maximum of one transmission block (or codeword) can betransmitted in a subframe k of a CC when the CC is configured as beingthe non-MIMO mode. Furthermore, it is assumed that a maximum of m (forexample, 2) transmission blocks (or codewords) can be transmitted in thesubframe k of a CC when the CC is configured as being the MIMO mode. Itis possible to know whether a CC is configured as being the MIMO mode,by using a transmission mode configured by a higher layer. Moreover, itis assumed that one (non-MIMO) or m (MIMO) ACK/NACK information signalsare generated depending on a transmission mode configured for the CCsirrespective of the number of actually transmitted transmission blocks(or codewords).

In the specification, HARQ-ACK represents a reception response resultfor a data block, that is, ACK/NACK/DTX response (simply, ACK/NACKresponse). The ACK/NACK/DTX response represents ACK, NACK and DTX orNACK/DTX. In addition, “HARQ-ACK for a specific CC” or “HARQ-ACK of aspecific CC” indicates ACK/NACK/DTX response (simply, ACK/NACK response)with respect to a data block (e.g. PDSCH) related to the CC (e.g.scheduled to the specific CC). Furthermore, an ACK/NACK state indicatesa combination corresponding to a plurality of HARQ-ACK signals. Here,the PDSCH may be substituted with a transmission block or codeword. InLTE-A, only self-carrier scheduling is possible for a DL PCC.Accordingly, the PDCCH that schedules the PDSCH on the DL PCC istransmitted only on the DL PCC. On the other hand, a DL SCC can becross-carrier scheduled. Accordingly, the PDCCH that schedules the PDSCHon the DL SCC is transmitted (cross-carrier scheduled) on the DL PCC ortransmitted (self-carrier scheduled) on the DL SCC.

To solve the aforementioned problem, when ACK/NACK selection is appliedto transmit a plurality of ACK/NACK information signals for a pluralityof CCs, the present invention suggests transmission of ACK/NACK using animplicit PUCCH resource (refer to Equation 1) linked to the PDCCH thatschedules the DL PCC if NACK or DTX is set for all CCs (i.e., DL SCCs)(in other words, DL SCells) other than the DL PCC when one or more CCsincluding at least the DL PCC (in other words, DL PCell) are scheduled.In other words, in ACK/NACK state mapping design, an ACK/NACK state inwhich “A” or “N” is for the DL PCC (or each CW of the DL PCC) and “N/D”is for all DL SCCs (or each CW of DL SCCs) is restricted such that theACK/NACK state uses an implicit PUCCH resource linked to the PDCCH forthe DL PCC according to the scheme defined in LTE instead of an explicitPUCCH resource (for convenience's sake, referred to as “PCC fallback”).In case of PCC fallback, a PUCCH format used to transmit the ACK/NACKstate and a modulation symbol transmitted through the PUCCH format maybe restricted such that they conform to the scheme defined by the LTE.For example, ACK/NACK can be transmitted using the PUCCH format 1billustrated in FIG. 7 and the modulation table (refer to Table 2) incase of PCC fallback.

More specifically, a case in which a PCC transmission mode is configuredas being the non-MIMO mode (single CW) is explained first. Two ACK/NACKstates in which “A” or “N” is for the PCC and “N/D” is for all SCCs (oreach CW of SCCs) are assumed. In this case, the ACK/NACK states aremapped to two constellation points on an implicit PUCCH resource linkedto the PDCCH that schedules the PCC. Here, the two constellation pointsfor the ACK/NACK states may be restricted such that they correspond totwo constellation points defined for PUCCH format 1a ACK/NACKtransmission for transmission of single CW in a single CC.Alternatively, the two constellation points for the ACK/NACK states maybe restricted such that they correspond to two constellation points for“AA” and “NN” among four constellation points defined for PUCCH format1b ACK/NACK transmission in a single CC. That is, mapping points of theACK/NACK states on the constellation are determined on the basis of “A”and “N” of the PCC. Preferably, the mapping points of the ACK/NACKstates on the constellation are restricted such that “A” and “N” of thePCC are located at the same positions as “A” and “N” for the PUCCHformat 1a or “AA” and “NN” for the PUCCH format 1b.

Next, a case in which the PCC transmission mode is configured as beingthe MIMO mode (e.g. two CWs or two TBs) is explained. Four ACK/NACKstates in which “A+A”, “A+N”, N+N”, or “N+N” is for the PCC and “N/D” isfor all SCCs (or each CW of SCCs) are supposed. In this case, theACK/NACK states are mapped to four constellation points on an implicitPUCCH resource linked to the PDCCH that schedules the PCC. Here, thefour constellation points for the ACK/NACK states correspond to fourconstellation points defined for PUCCH format 1b ACK/NACK transmissionwith respect to transmission of two CWs in a single CC. Mapping pointsof the ACK/NACK states on the constellation are determined on the basisof “A” and “N” of each CW of the PCC. In the specification, “N” of thePCC includes NACK, DTX or NACK/DTX. Preferably, “A” and “N” of each CWof the PCC are mapped to the same positions as “A” and “N” of each CWfor the PUCCH format 1b on the constellation.

FIG. 12 illustrates a PUCCH format 1a/1b based ACK/NACK selection methodfor single CW/two CWs in a single CC according to LTE. FIG. 13illustrates an ACK/NACK transmission method according to an embodimentof the present invention in the case that the PCC is configured tosupport the non-MIMO or MIMO transmission mode when three CCs (PCC, CC1and CC2) are aggregated. For convenience's sake, it is assumed that SCCs(i.e., CC1 and CC2) are configured to support the non-MIMO mode in thisembodiment.

Referring to FIGS. 12 and 13, “explicit ACK/NACK selection” is notapplied to ACK/NACK states in which “A” or “N” is for the non-MIMO modePCC and “N/D” is for all SCCs (that is, PCC fallback). That is, ACK/NACKstates in which (PCC, CC1, CC2)=(A, N/D, N/D) and (N, N/D, N/D) aremapped to an implicit PUCCH resource linked to the PDCCH that schedulesthe PCC and transmitted. In this case, the mapping relationship betweenthe ACK/NACK states and constellation points conforms to the LTEprinciple illustrated in FIG. 12.

Furthermore, “explicit ACK/NACK selection” is not applied to ACK/NACKstates in which “A+A”, “A+N”, “N+A, or “N+N” is for the MIMO mode PCCand “N/D” is for all the SCCs (That is, PCC fallback). In this case, themapping relationship between the ACK/NACK states and constellationpoints conforms to the LTE principle illustrated in FIG. 12 on the basisof ACK/NACK for the PCC. That is, the ACK/NACK states in which (PCC CW1,PCC CW2, CC1, CC2)=(A, A, N/D, N/D), (A, N, N/D, N/D), (N, A, N/D, N/D),and (N, N, N/D, N/D) are mapped to the implicit PUCCH resource linked tothe PDCCH that schedules the PCC and transmitted.

Even if the PCC is configured as being the MIMO mode, one or more PDSCHstransmitted on the PCC are scheduled through one PCC PDCCH. Accordingly,one implicit PUCCH resource is occupied for transmission of ACK/NACKrelated to the PCC.

Tables 4 and 5 show ACK/NACK state mapping tables. Tables 4 and 5 showsome ACK/NACK states, in which PCC fallback is performed. The mappingrelationship of PUCCH resources and bit values used to transmit otherACK/NACK states can be arbitrarily defined in the present invention.That is, the mapping relationship of PUCCH resources and bit values usedto transmit the other ACK/NACK states is “don't care” in the presentinvention.

TABLE 4 PCC SCC1 SCC2 HARQ- HARQ- HARQ- b(0), . . . , ACK(0) ACK(1)ACK(2) b(M_(bit) − 1) d(0) ACK NACK/DTX NACK/DTX 1 (11) −1 NACK NACK/DTXNACK/DTX 0 (00) +1

Here, HARQ-ACK(0) indicates ACK/NACK/DTX response to a CW (or TB) of thePCC. HARQ-ACK(1) indicates ACK/NACK/DTX response to the SCC1 andHARQ-ACK(2) indicates ACK/NACK/DTX response to CW1 of the SCC2. TheACK/NACK/DTX response includes ACK, NACK, and DTX or NACK/DTX. In thePCC, NACK includes NACK, DTX or NACK/DTX. d[0] corresponding to anACK/NACK state is transmitted using an implicit PUCCH resource, and theimplicit PUCCH resource is linked to the PDCCH used for PCC CW (or TB)scheduling (refer to Equation 1). The PUCCH formats 1a/1b, preferably,the PUCCH format 1b can be used.

TABLE 5 PCC SCC1 SCC2 HARQ- HARQ- HARQ- HARQ- b(0), . . . , ACK(0)ACK(1) ACK(2) ACK(3) b(M_(bit) − 1) d(0) ACK ACK NACK/DTX NACK/DTX 11 −1ACK NACK NACK/DTX NACK/DTX 10  j NACK ACK NACK/DTX NACK/DTX 01 −j NACKNACK NACK/DTX NACK/DTX 00  1

In Table 5, HARQ-ACK(0) indicates ACK/NACK/DTX response to CW1 (or TB1)of the PCC and HARQ-ACK(1) indicates ACK/NACK/DTX response to CW2 (orTB2) of the PCC. HARQ-ACK(2) indicates ACK/NACK/DTX response to the SCC1and HARQ-ACK(3) indicates ACK/NACK/DTX response to CW1 of the SCC2. TheACK/NACK/DTX response includes ACK, NACK, and DTX or NACK/DTX. In thePCC, NACK includes NACK, DTX or NACK/DTX. d(0) corresponding to anACK/NACK state is transmitted using an implicit PUCCH resource, and theimplicit PUCCH resource is linked to the PDCCH used for PCC CW (or TB)scheduling (refer to Equation 1). The PUCCH format 1b can be used.

FIG. 13 shows a case in which there are two SCCs configured to supportthe non-MIMO mode. FIG. 13 shows an exemplary case and the ACK/NACKtransmission method according to the present invention is not affectedby the number of SCCs and SCC transmission mode if ACK/NACK for all theSCCs is NACK/DTX. Accordingly, it is possible to prevent ACK/NACKresources from being wasted even though “explicit ACK/NACK selection” isemployed. Furthermore, inconsistency of ACK/NACK information on the PCCcan be solved even if there is CC configuration inconsistency betweenthe BS and UE during a CC reconfiguration process.

Additionally, when the PCC ACK/NACK transmission method using theimplicit PUCCH resources (that is, PCC fallback) is applied on the basisof the “explicit ACK/NACK selection”, the present invention suggests adetailed ACK/NACK state mapping method on explicit PUCCH resources. Forconvenience of explanation, only a case in which two independent CCs areaggregated is supposed in the following description. However, thesuggested method can be applied to three or more CCs. The two CCscorrespond to the PCC and SCC. According to the proposed method of thepresent invention, the UE selects one of PUCCH resources depending onthe A/N state and transmits b(0)b(1) (that is, d(0)) corresponding tothe A/N state using the selected PUCCH resource. It is assumed that thePUCCH format 1b is used.

FIGS. 14 a and 14 b illustrate methods of mapping A/N states to oneimplicit PUCCH resource (PUCCH #0) and three explicit PUCCH resources(PUCCHs #1, #2 and #3) when both the PCC and SCC are set to the MIMOtransmission mode (that is, four A/Ns need to be transmitted). The UEgenerates and transmits a PUCCH signal according to the shown mappingrule.

Referring to FIG. 14 a, ACK/NACK (A/N) states are mapped to the implicitresource PUCCH #0 according to the aforementioned PCC fallback method.Distinctly, an A/N state in which “D” is for the PCC and “NN” or “D” isfor the SCC, that is, (D, NN/D) is not transmitted. That is, the A/Nstate (D, NN/D) is not mapped to any implicit/explicit PUCCH resource.When this mapping method is generalized as “Method 1” for two or moreCCs, transmission of A/N state in which “D” is for the PCC and “NN”/“D”(MIMO CC) or “N”/“D” (non-MIMO CC) is for all the remaining CCs isdropped. Consequently, different PCC A/N states are mapped to differentconstellation points on the implicit resource. All SCC A/N statescorrespond to NN/D on all the constellation points of the implicitresource.

The implicit resource mapping structure can be applied without beingmodified when the remaining A/N states are mapped to the three explicitPUCCHs #1, #2 and #3. Different PCC A/N states may be mapped todifferent constellation points on the explicit resources. In addition,PCC A/N states mapped to the same constellation point on differentexplicit resources may be the same. Furthermore, the same SCC A/N statemay be mapped to all constellation points on an arbitrary explicitresource. Moreover, different SCC A/N states may be mapped to the sameconstellation points on different explicit resources. When this methodis generalized as “Method 2” irrespective of implicit/explicitresources, different PCC A/N states may be mapped to differentconstellation points on each PUCCH resource. PCC A/N states mapped tothe same constellation point on different PUCCH resources may be thesame. For the SCC, the same SCC A/N state can be mapped to allconstellation points on an arbitrary PUCCH resource. In addition,different SCC A/N states can be mapped to different PUCCH resources.

FIG. 14 b illustrates an A/N state mapping method when the CC sequence(PCC, SCC) in the A/N states shown in FIG. 14 a is changed to (SCC,PCC).

Table 6 shows an A/N state mapping table based on the method of FIG. 14a. Table 6 shows some of A/N states for ACK/NACK selection, in which PCCfallback is performed, when the ACK/NACK selection is carried out usingfour PUCCH resources. The mapping relationship of PUCCH resources andbit values used to transmit the remaining ACK/NACK states can bearbitrarily defined in the present invention. That is, the mappingrelationship of PUCCH resources and bit values used to transmit theremaining ACK/NACK states is “don't care” in the present invention.

TABLE 6 PCC SCC HARQ- HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2) ACK(3) n⁽¹⁾_(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACKNACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX NACK/DTXn⁽¹⁾ _(PUCCH, 0) 01 NACK NACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00

Here, HARQ-ACK(0) indicates ACK/NACK/DTX response to CW1 (or TB1) of thePCC and HARQ-ACK(1) indicates ACK/NACK/DTX response to CW2 (or TB2) ofthe PCC. Similarly, HARQ-ACK(2) represents ACK/NACK/DTX response to CW1(or TB1) of the SCC and HARQ-ACK(3) represents ACK/NACK/DTX response toCW2 (or TB2) of the SCC. The ACK/NACK/DTX response includes ACK, NACK,and DTX or NACK/DTX. For the PCC, NACK includes NACK, DTX or NACK/DTX.In addition, n⁽¹⁾ _(PUCCH, i) (i=0, 1, 2, 3) indicates a plurality ofPUCCH resource indexes occupied for ACK/NACK selection (refer toEquation 1), and n⁽¹⁾ _(PUCCH, 0) indicates a PUCCH resource indexlinked to the PDCCH used for PCC CW (or TB) scheduling (refer toEquation 1). Furthermore, b(0)b(1) corresponding to the ACK/NACK stateis transmitted using an implicit PUCCH resource. The b(0)b(1) can betransmitted through the PUCCH format 1b. In this case, the PUCCHresource indicates the PUCCH resource for the PUCCH format 1b.

FIG. 15 a illustrates an example of mapping A/N states to one implicitPUCCH resource (PUCCH #0) and one explicit PUCCH resource (PUCCH #1)when the PCC and SCC are respectively set to the MIMO and non-MIMOtransmission modes (i.e. three A/Ns need to be transmitted). The UEgenerates and transmits a PUCCH signal according to the illustratedmapping rule. Referring to FIG. 15 a, all the above-described PCCfallback method, Method 1 (i.e., A/N state in which D is for the PCC andN/D is for the SCC is not transmitted), and Method 2 (i.e., PCC A/Nstates are discriminated using different constellation points and SCCA/N states are discriminated using different PUCCH resources) areapplied to the mapping method. FIG. 15 b illustrates an A/N statemapping method when the CC sequence (PCC, SCC) in the A/N states shownin FIG. 15 a is changed to (SCC, PCC).

FIG. 16 a illustrates an example of mapping A/N states to one implicitPUCCH resource (PUCCH #0) and two explicit PUCCH resources (PUCCHs #1and #2) when the PCC and SCC are respectively set to the non-MIMO andMIMO transmission modes (i.e. transmission of three A/N states isneeded). In this case, the PCC fallback method may be followed by Method2 in which the PCC and SCC mapping rule has been modified only for theexplicit resources, as illustrated in FIG. 16 a. When this method isgeneralized as “Method 2a” for explicit resource mapping of non-MIMO PCCand MIMO SCC, different SCC A/N states may be mapped to differentconstellation points on each explicit PUCCH resource and SCC A/N statesmapped to the same constellation points on different explicit resourcesmay be the same. In the case of PCC, the same PCC A/N state may bemapped to all constellation points on an arbitrary explicit PUCCHresource and different PCC A/N states may be mapped to differentexplicit PUCCH resources. Method 1 can be applied to an A/N state havingthe PCC and SCC corresponding to (D, NN/D) without being modified.

In this case, constellation points having no previously mapped A/N statemay exist on the explicit resources. Accordingly, it is possible toadditionally map the A/N state (D, NN/D) to one of the correspondingconstellation points. When this method is generalized as “Method 1a”, anA/N state in which “D” is for the PCC and “NN”/“D” (MIMO CC) or “N”/“D”(non-MIMO CC) is for the remaining CCs can be mapped to one of unmappedavailable constellation points on the explicit PUCCH resources to whichMethod 2/2a are applied.

FIG. 16 b illustrates an A/N state mapping method when the CC sequence(PCC, SCC) in the A/N states shown in FIG. 16 a is changed to (SCC,PCC).

FIG. 17 a illustrates a method of mapping A/N states to one implicitPUCCH resource (PUCCH #0) and one explicit PUCCH resource (PUCCH #1)when the PCC and SCC are respectively set to the non-MIMO and MIMOtransmission modes (i.e. three A/N states need to be transmitted).

Referring to FIG. 17 a, after application of the PCC fallback method andMethod 1, A/N states can be additionally mapped to unmapped availableconstellation points on the implicit resource to reduce use of explicitresource. Here, since only A/N states in which “D” is not set for thePCC can be mapped to the implicit resource, it is preferable to map someof A/N states in which “A” is set for the PCC to the implicit resourcein consideration of resource increase due to N/D decoupling. When thismethod is generalized as “Method 2b” for mapping A/N states of non-MIMOPCC and MIMO SCC, some of the A/N states in which “A” is set for the PCCare mapped to unmapped available constellation points on the implicitPUCCH resource to which the PCC fallback has been applied.

FIG. 17 b illustrates an A/N state mapping method when the CC sequence(PCC, SCC) in the A/N states shown in FIG. 17 a is changed to (SCC,PCC).

FIG. 18 a illustrates a method of mapping A/N states to one implicitPUCCH resource (PUCCH #0) and one explicit PUCCH resource (PUCCH #1)when both the PCC and SCC are set to the non-MIMO mode (i.e.transmission of two A/N states is required). Referring to FIG. 18, allthe PCC fallback method, Method 1 or Method 1a (an A/N state having thePCC and SCC corresponding to (D, N/D) is not transmitted or it is mappedto the remaining explicit resource), and Method 2 are applied to themapping method.

FIG. 18 b illustrates an A/N state mapping method when the CC sequence(PCC, SCC) in the A/N states shown in FIG. 18 a is changed to (SCC,PCC).

When “explicit ACK/NACK selection” to which the proposed PCC fallbackmethod, Method 1/1a, and Method 2/2a/2b are applied is performed totransmit a plurality of ACK/NACK states, it is possible to efficientlytransmit the ACK/NACK states while minimizing PUCCH resource overhead.

Moreover, an ACK/NACK selection method that uses both the implicit PUCCHresource linked to the PDSCH scheduling the PCC and the implicit PUCCHresource linked to the PDCCH scheduling the SCC may be considered. Whentwo CWs (or two TBs) are transmitted through an arbitrary MIMOtransmission mode CC, the PDCCH that schedules the CC, that is, DCIformat has relatively large payload, and thus the PDCCH can be encodedto higher than a 2 CCE aggregation level. Accordingly, when the two CWs(or two TBs) are transmitted through the MIMO transmission mode CC, itmay be possible to consider use of two implicit PUCCH resources (i.e.implicit PUCCH resources #1 and #2) which are respectively linked to thelowest CCE index nPDCCH of the PDCCH that schedules the CC and the nextindex nPDCCH+1. When a single CW (or a single TB) is transmitted througha MIMO mode CC or a non-MIMO mode CC, it may be possible to consider useof only one implicit PUCCH resource (i.e., implicit PUCCH resources #1)linked to the lowest CCE index nPDCCH of the PDCCH that schedules theCC. This condition is referred to as “condition #1” for convenience ofexplanation.

When a single CW is transmitted through an arbitrary MIMO mode CC afteran A/N state mapping table considering transmission of two CWs in allMIMO mode CCs is generated, a method of reusing some of the mappingtable (preferably, half the mapping table) may be considered.Specifically, two A/N states having ACK or NACK for single CWtransmission in an MIMO mode CC may be mapped to two of four A/N statesof AA, AN, NA and NN for transmission of two CWs in the correspondingCC. In consideration of ACK/NACK constellation of the PUCCH format 1a/1bfor single CW transmission in LTE, A and N for a single CW of an MIMOmode CC can be respectively mapped to AA and NN for two CWs of thecorresponding CC (Alta). In addition, when a signal CW is transmitted,it is possible to consider the CW as the first CW in the case oftransmission of two CWs and process the second CW as NACK. That is, Aand N for the single CW of the MIMO mode CC can be respectively mappedto AN and NN for the two CWs of the corresponding CC (Alt2).

It is assumed that Alt1 is employed in the specification unlessmentioned otherwise. Here, when the single CW is transmitted under theabove condition, only the implicit PUCCH #1 linked to the lowest CCEindex of the PDCCH that schedules the MIMO mode CC can be used.Accordingly, an A/N state in which AA or NN is set for the correspondingCC cannot be mapped/transmitted to the implicit PUCCH #2 linked to thePDCCH that schedules the corresponding CC (i.e. linked to thecorresponding CC). When this method is generalized as “Method 3”, an A/Nstate used for single CW transmission for an arbitrary MIMO mode CCcannot be mapped/transmitted to the implicit PUCCH #2 linked to thecorresponding CC.

Under this condition, the A/N state mapping rule for implicit PUCCHresource based ACK/NACK selection can be arranged as follows.

1) Application of the Suggested PCC Fallback Method

-   -   An A/N state in which A, N, or AA, AN, NA, NN is set for the PCC        and N/D or NN/D is set for the remaining CCs is mapped to PCC        PUCCH #1.

2) Application of the Suggested Method 1

-   -   An A/N state in which D is set for the PCC and N/D or NN/D is        set for the remaining CCs is not transmitted and mapped to any        PUCCH resource.

3) Application of Implicit PUCCH Resource Mapping (“Implicit MappingRule”)

-   -   An A/N state in which N/D or NN/D is set for an arbitrary CC        cannot be mapped/transmitted to any implicit PUCCH resource        linked to the corresponding CC.

4) Application of the Suggested Method 3

-   -   An A/N state used to transmit a single CW for an MIMO mode CC        (e.g. an A/N state in which AA and NN are set for two CWs of the        corresponding CC) cannot be mapped/transmitted to the implicit        PUCCH #2 linked to the corresponding CC.

As described above with reference to FIG. 11, a DL CC set aggregated bythe UE in LTE-A can be UE-specifically allocated through RRC signaling.When the DL CC set is reconfigured using RRC signaling, an A/N feedbackrelated operation may not be normally performed since a DL CC set (orthe number of DL CCs) recognized by the BS differs from a DL CC set (orthe number of DL CCs) recognized by the UE (i.e. misaligned) in thereconfiguration period. However, the suggested PCC fallback method canprevent misalignment between the BS and UE for at least PCC A/N stateeven if the DL CC set is changed through RRC signaling thereby themapping rule (e.g. mapping table) for A/N selection is to be changed.Furthermore, differently from Alt2, Alt1 can prevent misalignmentbetween the BS and UE with respect to PCC A/N state mapping irrespectiveof whether two CWs (or two TBs) are transmitted or a single CW (orsingle TB) is transmitted for the PCC even if the DL CC set is changedfrom a plurality of DL CCs to one PCC through RRC signaling.

FIG. 19 illustrates an A/N state mapping method when both the PCC andSCC are set to the MIMO mode (i.e. four A/N states need to betransmitted). This mapping method uses two PUCCH resources (referred toas PCC PUCCHs #1 and #2 hereinafter) occupied for ACK/NACK with respectto two CWs (or two TBs) of the PCC and two PUCCH resources (referred toas SCC PUCCHs #1 and #2 hereinafter) occupied for ACK/NACK with respectto two CWs (or two TBs) of the SCC. The PCC PUCCHs #1 and #2 may beimplicitly given. The SCC PUCCHs #1 and #2 may be given implicitly orexplicitly.

Referring to FIG. 19, an A/N state is mapped to the PCC PUCCH #1 byapplying the suggested PCC fallback method and Method 1. Then, theremaining A/N states are mapped to the remaining three resources (PCCPUCCH #2, SCC PUCCH #1 and SCC PUCCH #2) according to the implicitmapping rule and Method 3. Specifically, an A/N state used in a case ofa single CW transmission of the PCC, that is, an A/N state AA and NN fortwo PCC CWs, is not mapped to the PCC PUCCH #2. Similarly, an A/N stateused in a case of a single CW transmission of the SCC, that is, an A/Nstate AA and NN for two SCC CWs, is not mapped to the SCC PUCCH #2.

FIG. 20 illustrates an A/N state mapping method when two CCs arerespectively set to the MIMO and non-MIMO transmission modes (i.e. threeA/N states need to be transmitted). This mapping method uses two PUCCHresources (referred to as MCC PUCCHs #1 and #2 hereinafter) occupied forACK/NACK with respect to two CWs (or two TBs) of the MIMO mode CC(referred to as MCC hereinafter) and one PUCCH resource (referred to asnon-MCC PUCCH hereinafter) occupied for ACK/NACK with respect to a CW(or TB) of the non-MIMO mode CC (referred to as non-MCC hereinafter).The PUCCH resources may be given explicitly or implicitly.

Referring to FIG. 20, A/N states AA+N/D, AN+N/D, NA+N/D, and NN+N/D forMCC+non-MCC can be mapped to the MCC PUCCH #1 by using the proposed PCCfallback method in consideration of the PCC in the MIMO mode.Furthermore, A/N states NN/D+A (or NN/DD+A) and NN/D+N (or NN/DD+N)) forMCC+non-MCC can be mapped to the non-MCC PUCCH by using the suggestedPCC fallback method in consideration of the PCC in the non-MIMO mode(Alt a).

Here, when NN+N/D (i.e. NNN and NND) is mapped to the MCC PUCCH #1 andNN/D+N (i.e. NNN and DN (or DDN)) is mapped to the non-MCC PUCCH forMCC+non-MCC, as described above, a specific state, for example, NN+N isrepeated and the BS may need to perform blind decoding on this specificstate. Furthermore, as the same A/N state (i.e., NN+N) is repeatedlymapped to different PUCCH resources, one A/N state that can betransmitted by the UE to the BS is wasted.

To prevent this, it may be possible to map NN+N/D to the MCC PUCCH #1and map only D+N (or DD+N) from NN/D+N (or NN/DD+N) to the non-MCC PUCCH(Alt b). According to Alt b, whether DTX is set for the MCC can becorrectly fed back since only D+N (or DD+N) from NN/D+N (or NN/DD+N) istransmitted on the non-MCC PUCCH. Accordingly, Alt b is advantageouswhen the PCC operates in the MIMO mode in terms of DTX feedback for thePCC. On the contrary, a method of mapping NN+N/D to the MCC PUCCH #1 andmapping only NN+D from NN+N/D to the non-MCC PUCCH can be considered(Alt c). According to Alt c, whether DTX is set for the non-MCC can becorrectly fed back since only NN+D from NN+N/D is transmitted on the MCCPUCCH. Accordingly, Alt c is advantageous when the PCC operates in thenon-MIMO mode in terms of DTX feedback for the PCC.

When this method is generalized as “Method 1b”, if an A/N state in whichA, N, or AA, AN, NA, NN is set for a specific CC (i.e., XCC) and N/D orNN/D is set for other CCs is mapped to implicit PUCCH #1 linked to theXCC, an A/N state in which D is set for the XCC and N or NN is set forall the remaining CCs can be mapped/transmitted to one of implicit PUCCHresources #1 linked to the remaining CCs. If Method 1b is employed whenthe XCC is considered as the PCC, application of the suggested Method 1may be omitted.

Consequently, the proposed PCC fallback operation can be performedirrespective of whether the PCC is set to the MIMO mode or non-MIMO modein any of cases in which Alt a, Alt b and Alt c are applied. Accordingto the present invention, a normal operation can be performed withoutinconsistency between the BS and UE for at least PCC A/N states at leastin the RRC reconfiguration period. Subsequently, the remaining three A/Nstates AA+A, AN+A and NA+A with respect to MCC+non-MCC are mappedaccording to the implicit mapping rule and Method 3. Specifically, anA/N state used in a case of a single CW (or TB) transmission of the MCC,that is, an A/N state in which AA and NN are set for two CWs (or twoTBs) of the MCC, is not mapped to MCC PUCCH #2.

Tables 7, 8 and 9 show A/N state mapping tables according to the mappingmethod of FIG. 20. Tables 7, 8 and 9 respectively correspond to Alt 1,Alt 2 and Alt3. Table 7, 8 and 9 show some of A/N states for ACK/NACKselection, in which the PCC fallback is performed. The mappingrelationship of PUCCH resources and bit values used to transmit theremaining ACK/NACK states can be arbitrarily defined in the presentinvention. That is, the mapping relationship of PUCCH resources and bitvalues used to transmit the remaining ACK/NACK states is “don't care” inthe present invent. Tables 7, 8 and 9 show cases in which ACK/NACKselection is performed using three PUCCH resources.

TABLE 7 MCC HARQ- HARQ- Non-MCC ACK(0) ACK(1) HARQ-ACK(2) n⁽¹⁾_(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACK NACKNACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 01 NACKNACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00 NACK/DTX NACK/DTX ACK n⁽¹⁾ _(PUCCH, 2)11 NACK/DTX NACK/DTX NACK n⁽¹⁾ _(PUCCH, 2) 00

TABLE 8 MCC HARQ- HARQ- Non-MCC ACK(0) ACK(1) HARQ-ACK(2) n⁽¹⁾_(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACK NACKNACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 01 NACKNACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00 NACK/DTX NACK/DTX ACK n⁽¹⁾ _(PUCCH, 2)11 DTX DTX NACK n⁽¹⁾ _(PUCCH, 2) 00

TABLE 9 MCC HARQ- HARQ- Non-MCC ACK(0) ACK(1) HARQ-ACK(2) n⁽¹⁾_(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACK NACKNACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 01 NACKNACK DTX n⁽¹⁾ _(PUCCH, 0) 00 NACK/DTX NACK/DTX ACK n⁽¹⁾ _(PUCCH, 2) 11NACK/DTX NACK/DTX NACK n⁽¹⁾ _(PUCCH, 2) 00

Here, HARQ-ACK(0) indicates ACK/NACK/DTX response to CW1 (or TB1) of theMCC and HARQ-ACK(1) indicates ACK/NACK/DTX response to CW2 (or TB2) ofthe MCC. HARQ-ACK(2) indicates ACK/NACK/DTX response to a CW (or TB) ofthe non-MCC. The ACK/NACK/DTX response includes ACK, NACK, and DTX orNACK/DTX. The non-MCC is an SCC if the MCC is a PCC. On the contrary,the MCC is an SCC if the non-MCC is a PCC. In the tables, NACK includesNACK, DTX or NACK/DTX, n⁽¹⁾ _(PUCCH, i) (i=0, 1, 2) indicates aplurality of PUCCH resource indexes occupied for ACK/NACK selection.n⁽¹⁾ _(PUCCH, 0) indicates a PUCCH resource index occupied for ACK/NACKwith respect to CW1 (or TB1) of the MCC. n⁽¹⁾ _(PUCCH, 2) indicates aPUCCH resource index occupied for ACK/NACK with respect to the CW (orTB) of the non-MCC. n⁽¹⁾ _(PUCCH, i) (i=0, 1, 2) may be explicitly givenor implicitly given according to the LTE method (refer to Equation 1).Data bits b(0)b(1) corresponding to ACK/NACK states is transmitted usingimplicit PUCCH resources. The data bits b(0)b(1) may be transmittedusing the PUCCH format 1b. In this case, PUCCH resources indicate PUCCHresources for the PUCCH format 1b.

FIG. 21 shows an A/N state mapping method when both the PCC and SCC areset to the non-MIMO transmission mode (i.e., two A/Ns needs to betransmitted). The mapping method uses one PUCCH resource (referred to asPCC PUCCH hereinafter) occupied for ACK/NACK with respect to a CW (orTB) of the PCC and one PUCCH resource (referred to as SCC PUCCHhereinafter) occupied for ACK/NACK with respect to a CW (or TB) of theSCC. The PCC PUCCH may be implicitly given. The SCC PUCCH may be givenexplicitly or implicitly.

Referring to FIG. 21, an A/N state may be mapped to the PCC PUCCH byusing the above suggested PCC fallback method, and an A/N state in whichD+N is set for PCC+SCC may be mapped to the SCC PUCCH using the proposedMethod 1b. Then, the remaining two A/N states A+A and N/D+A for thePCC+SCC may be mapped according to the aforementioned implicit mappingrule.

Table 10 shows an A/N state mapping table according to the method ofFIG. 21. Table 10 shows some of A/N states for ACK/NACK selection, inwhich the PCC fallback is performed. The mapping relationship of PUCCHresources and bit values used to transmit the remaining ACK/NACK statescan be arbitrarily defined in the present invention. That is, themapping relationship of PUCCH resources and bit values used to transmitthe remaining ACK/NACK states is “don't care” in the present invent.Table 10 shows a case in which ACK/NACK selection is performed using twoPUCCH resources.

TABLE 10 PCC SCC HARQ-ACK(0) HARQ-ACK(1) n⁽¹⁾ _(PUCCH, i) b(0)b(1) ACKNACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 NACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00

Here, HARQ-ACK(0) indicates ACK/NACK/DTX response to a CW (or TB) of thePCC and HARQ-ACK(1) indicates ACK/NACK/DTX response to a CW (or TB) ofthe SCC. The ACK/NACK/DTX response includes ACK, NACK, and DTX orNACK/DTX. n⁽¹⁾ _(PUCCH, i) (i=0, 1) indicates a plurality of PUCCHresource indexes occupied for ACK/NACK selection. n⁽¹⁾ _(PUCCH, 0)indicates a PUCCH resource index occupied for ACK/NACK with respect tothe CW (or TB) of the PCC. n⁽¹⁾ _(PUCCH, 1) indicates a PUCCH resourceindex occupied for ACK/NACK with respect to the CW (or TB) of the SCC.n⁽¹⁾ _(PUCCH, 0) may be implicitly given (refer to Equation 1). n⁽¹⁾_(PUCCH, 1) may be given explicitly or implicitly. Data bits b(0)b(1)may be transmitted using the PUCCH format 1b. In this case, PUCCHresources indicate PUCCH resources for the PUCCH format 1b.

As another ACK/NACK selection method using implicit PUCCH resources, amethod using two implicit PUCCHs #1 and #2 respectively linked to thelowest CCE index n_(PDCCH) and the next index n_(PDCCH)+1 of a PDCCHthat schedules a CC irrespective of the number of transmitted CWs whenthe CC is set to the MIMO transmission mode can be considered.Furthermore, in the case of a non-MIMO CC, use of only one implicitPUCCH #1 linked to the lowest CCE index n_(PDCCH) of a PDCCH thatschedules the corresponding CC can be considered. In this case,application of the proposed Method 3 to the implicit PUCCH #2 isunnecessary. In other words, an A/N state used in a case of a single CWtransmission for an arbitrary MIMO mode CC (e.g. an A/N state in whichAA and NN are set for two CWs of the corresponding CC) can bemapped/transmitted to/using any implicit PUCCH resource as long as theA/N state observes the implicit mapping rule. This condition is referredto as “condition #2” for convenience of explanation.

Under this condition, the A/N state mapping rule for implicit PUCCHresource based ACK/NACK selection can be arranged as follows byexcluding the suggested Method 3.

1) Application of the Proposed PCC Fallback Method

-   -   An A/N state in which A, N, or AA, AN, NA, NN is set for the PCC        and N/D or A/N is set for the remaining CCs is mapped to the PCC        PUCCH #1.

2) Application of the Proposed Method 1 or Method 1b

-   -   Method 1: An A/N state in which D is set for the PCC and N/D or        NN/D is set for the remaining CCs is not transmitted and mapped        to any PUCCH resource.    -   Method 1b: When an A/N state in which A, N, or AA, AN, NA, NN is        for a specific CC (i.e., XCC) and N/D or NN/D is set for all the        remaining CCs is mapped to the implicit PUCCH #1 linked to the        XCC and transmitted, an A/N state in which D is set for the XCC        and N or NN is set for the remaining CCs can be        mapped/transmitted to/using one of implicit PUCCHs #1 linked to        the remaining CCs. Here, the XCC may be a PCC.

3) Application of Implicit PUCCH Resource Mapping (“Implicit MappingRule”)

-   -   An A/N state in which N/D or NN/D is set for an arbitrary CC        cannot be mapped/transmitted to any implicit PUCCH resource        linked to the corresponding CC.

4) Application of Constellation Mapping that Minimizes A/N Error(“Gray-Like Mapping”)

-   -   A/N states mapped to adjacent symbols on an arbitrary PUCCH        resource constellation are mapped such that A/N error is        minimized (i.e., A-to-N/D error or N/D-to-A error is minimized        in the event of error detection between the A/N states).

FIG. 22 illustrates a method (ACK/NACK selection method) of mapping anA/N state to a PUCCH resource selected from among a plurality of PUCCHresources when both the PCC and SCC are set to the MIMO mode. Thismapping method uses two PUCCH resources (referred to as PCC PUCCHs #1and #2 hereinafter) occupied for ACK/NACK with respect to two CWs (ortwo TBs) of the PCC and two PUCCH resources (referred to as SCC PUCCHs#1 and #2 hereinafter) occupied for ACK/NACK with respect to two CWs (orTBs) of the SCC. The PCC PUCCHs #1 and #2 may be implicitly given. TheSCC PUCCHs #1 and #2 may be given explicitly or implicitly.

Referring to FIG. 22, an A/N state is mapped to the PCC PUCCH #1 byusing the proposed PCC fallback method and Method 1. Then, other A/Nstates are mapped to other three resources according to the implicitmapping rule and gray-like mapping.

FIG. 23 illustrates a method of mapping an A/N state to a PUCCH resourceselected from among a plurality of PUCCH resources when two CCs arerespectively set to the MIMO and non-MIMO modes. This mapping methoduses two PUCCH resources (referred to as MCC PUCCHs #1 and #2hereinafter) occupied for ACK/NACK with respect to the two CWs (or twoTBs) of the MIMO mode CC (referred to as MCC hereinafter) and one PUCCHresource (referred to as non-MCC PUCCH hereinafter) occupied forACK/NACK with respect to a CW (or PB) of the non-MIMO mode CC (referredto as non-MCC). The PCC PUCCHs may be given explicitly or implicitly.

Referring to FIG. 23, it is possible to consider A/N state mapping thatapplies the proposed PCC fallback method to the MCC PUCCH #1 inconsideration of the PCC in the MIMO mode and also applies the proposedPCC fallback method to the non-MCC PUCCH in consideration of the PCC inthe non-MIMO mode (application of Alt a). Here, considering the XCC asthe MCC for application of the proposed Method 1b (particularly, whenthe PCC is set to the MIMO mode), NN+N/D can be mapped to the MCC PUCCH#1 and D+N can be mapped to the non-MCC PUCCH for MCC+non-MCC. On thecontrary, considering the XCC as the non-MCC (particularly, when the PCCis set to the non-MIMO mode), NN/D+N can be mapped to the non-MCC PUCCHand NN+D can be mapped to the MCC PUCCH #1 for the MCC+non-MCC(application of Alt b and Alt c). The proposed PCC fallback operationcan be performed irrespective of whether the PCC is set to the MIMO modeor non-MIMO mode in any of cases in which Alt a, Alt b and Alt c areapplied. According to the present invention, a normal operation can beperformed without inconsistency between the BS and UE for at least PCCA/N states at least in the RRC reconfiguration period. Subsequently, theremaining A/N states can be mapped according to the implicit mappingrule and gray-link mapping.

FIG. 24 illustrates a method of mapping an A/N state to a PUCCH resourceselected from among a plurality of PUCCH resources when both the PCC andSCC are set to non-MIMO mode. This mapping method uses one PUCCHresource (referred to as PCC PUCCH hereinafter) occupied for ACK/NACKwith respect to a CW (or TB) of the PCC and one PUCCH resource (referredto as SCC PUCCH hereinafter) occupied for ACK/NACK with respect to a CW(or PB) of the SCC. The PCC PUCCH may be given implicitly. The SCC PUCCHmay be given explicitly or implicitly.

Referring to FIG. 24, an A/N state in which D+N is set for PCC+SCC canbe mapped by applying the suggested PCC fallback method to the PCC PUCCHand applying the proposed Method 1b to the SCC PUCCH. Then, the otherA/N state can be mapped according to the implicit mapping rule andgray-like mapping. In this case, a final A/N state mapping result may besimilar or equal to the above condition #1 based A/N state mappingresult.

As another ACK/NACK selection method using implicit PUCCH resources, amethod using only the implicit PUCCH resource linked to the lowest CCEindex n_(PDCCH) of a PDCCH that schedules an arbitrary CC irrespectiveof transmission mode for the CC can be considered. Furthermore, when thenumber of MIMO mode CCs is M, it is possible to consider use of Mexplicit PUCCH resources together with the implicit PUCCH resource. Inthis case, it is not necessary to apply/observe the proposed Method 3and implicit mapping rule for the explicit PUCCH resources. Thiscondition is referred to as “condition #3” for convenience ofexplanation.

Under this condition, the A/N state mapping rule for implicit PUCCHresource based ACK/NACK selection can be arranged as follows byexcluding the suggested Method 3 and the implicit mapping rule.

1) Application of the Proposed PCC Fallback Method

-   -   An A/N state in which A, N, or AA, AN, NA, NN is set for the PCC        and N/D or A/N is set for all the remaining CCs is mapped to the        PCC PUCCH #1.

2) Application of the Proposed Method 1 or Method 1b

-   -   Method 1: An A/N state in which D is set for the PCC and N/D or        NN/D is set for all the remaining CCs is not transmitted and        mapped to any PUCCH resource.    -   Method 1b: When an A/N state in which A, N, or AA, AN, NA, NN is        set for a specific CC (i.e., XCC) and N/D or NN/D is set for all        the remaining CCs is mapped to the implicit PUCCH #1 linked to        the XCC and transmitted, an A/N state in which D is set for the        XCC and N or NN is set for all the remaining CCs can be        mapped/transmitted to one of implicit PUCCHs #1 linked to the        remaining CCs. Here, the XCC may be a PCC.

3) Application of Constellation Mapping that Minimizes A/N Error(“Gray-Like Mapping”)

-   -   A/N states mapped to adjacent symbols on an arbitrary PUCCH        resource constellation are mapped such that A/N error is        minimized (i.e., A-to-N/D error or N/D-to-A error is minimized        in the event of error detection between the A/N states).

On the basis of the above mapping rule, A/N state mapping results forthree cases (a case in which both the PCC and SCC are set to the MIMOmode, a case in which two CCs are respectively set to the MIMO andnon-MIMO modes, and a case in which the both the PCC and SCC are set tothe non-MIMO mode) may be similar or equal to the above condition #2based A/N state mapping results (FIGS. 22, 23 and 24).

FIG. 25 shows a BS and a UE applicable to an embodiment of the presentinvention. If a wireless communication system includes a relay,communication is carried out between a BS and the relay on backhaul linkand communication is performed between the relay and a UE on accesslink. Accordingly, the BS and UE shown in the figure may be substitutedby the relay depending on the circumstance.

Referring to FIG. 25, a wireless communication system includes the BS100 and UE 120. The BS 100 includes a processor 112, a memory 114 and aradio frequency (RF) unit 116. The processor 112 may be configured suchthat it implements the procedures and/or methods suggested by thepresent invention. The memory 114 is connected to the processor 112 andstores information regarding the operation of the processor 112. The RFunit 116 is connected to the processor 112 and transmits and/or receivesRF signals. The UE 120 may be configured such that it implements theprocedures and/or methods proposed by the present invention. The UEincludes a processor 122, a memory 124 and an RF unit 126. The process122 may be configured such that it implements the procedures and/ormethods suggested by the present invention. The memory 124 is connectedto the processor 122 and stores information regarding the operation ofthe processor 122. The RF unit 126 is connected to the processor 122 andtransmits and/or receives RF signals. The BS 100 and/or the UE 120 mayinclude a single antenna or multiple antennas.

The aforementioned embodiments are achieved by combination of elementsand features of the present invention in a predetermined manner. Each ofthe elements or features should be considered selectively unlessspecified separately. Each of the elements or features may be carriedout without being combined with other elements or features. Also, someelements and/or features may be combined with one another to constitutethe embodiments of the present invention. The order of operationsdescribed in the embodiments of the present invention may be changed.Some elements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. It will be apparent that claims whichare not explicitly dependent on each other can be combined to provide anembodiment or new claims can be added through amendment after thisapplication is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between a base station and a userequipment. In this case, the base station means a terminal node of anetwork, which performs direct communication with the mobile station. Aspecific operation which has been described as being performed by thebase station may be performed by an upper node of the base station asthe case may be. In other words, it will be apparent that variousoperations performed for communication with the mobile station in thenetwork which includes a plurality of network nodes along with the basestation may be performed by the base station or network nodes other thanthe base station. The base station may be replaced with terms such asfixed station, Node B, eNode B (eNB), and Access Point (AP). Also, theuser equipment may be replaced with terms such as Subscriber Station(SS), Mobile Subscriber Station (MSS), Mobile Terminal (MT) and aterminal.

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, or combinationthereof. In a hardware configuration, the embodiments of the presentinvention may be implemented by one or more Application SpecificIntegrated Circuits (ASICs), Digital Signal Processors (DSPs), DigitalSignal Processing Devices (DSPDs), Programmable Logic Devices (PLDs),Field Programmable Gate Arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, the embodiments of the presentinvention can be implemented by a type of a module, a procedure, or afunction, which performs functions or operations described above.Software code may be stored in a memory unit and then may be executed bya processor. The memory unit may be located inside or outside theprocessor to transmit and receive data to and from the processor throughvarious means which are well known.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific forms than those set forth herein withoutdeparting from the spirit and essential characteristics of the presentinvention. The above description is therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by reasonable interpretation of the appended claimsand all changes coming within the equivalency range of the invention areintended to be within the scope of the invention.

The present invention can be used in a wireless communication systemsuch as UE, relay, BS, etc.

1. A method for transmitting uplink control information in a situationin which a plurality of cells including a primary cell and a secondarycell is configured in a wireless communication system, the methodcomprising: selecting one PUCCH resource corresponding to a plurality ofHARQ-ACKs (Hybrid Automatic Repeat reQuest-Acknowledgements) from aplurality of PUCCH resources for PUCCH (Physical Uplink Control Channel)format 1; and transmitting bit values corresponding to the plurality ofHARQ-ACKs using the selected PUCCH resource, wherein the relationshipamong the plurality of HARQ-ACKs, PUCCH resource and bit values includesthe relationship of the following Table 1 TABLE 1 HARQ-ACK(0)HARQ-ACK(1) n⁽¹⁾ _(PUCCH, i) b(0)b(1) ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11NACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00

where HARQ-ACK(0) indicates ACK/NACK/DTX response to a data blockrelated to the primary cell, HARQ-ACK(1) indicates ACK/NACK/DTX responseto a data block related to the secondary cell, n⁽¹⁾ _(PUCCH, i) (i=0, 1)indicates a plurality of PUCCH resources for the PUCCH format 1, n⁽¹⁾_(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH (PhysicalDownlink Control Channel) on the primary cell, and b(0)b(1) indicatesthe bit values.
 2. The method according to claim 1, wherein therelationship among the plurality of HARQ-ACKs, PUCCH resource and bitvalues further includes the relationship of the following Table 2 TABLE2 HARQ- HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2) ACK(3) n⁽¹⁾ _(PUCCH, i)b(0)b(1) ACK ACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11 ACK NACK NACK/DTXNACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0)01 NACK NACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00

where HARQ-ACK(0)(1) indicates ACK/NACK/DTX responses to data blocksrelated to the primary cell, HARQ-ACK(2)(3) indicates ACK/NACK/DTXresponses to data blocks related to the secondary cell, n⁽¹⁾ _(PUCCH, i)(i=0, 1, 2, 3) indicates a plurality of PUCCH resources for the PUCCHformat 1, n⁽¹⁾ _(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH(Physical Downlink Control Channel) on the primary cell, and b(0)b(1)indicates the bit values.
 3. The method according to claim 1, whereintransmission of the plurality of HARQ-ACKs is dropped if HARQ-ACK(0) isDTX and HARQ-ACK(1) is NACK.
 4. The method according to claim 2, whereintransmission of the plurality of HARQ-ACKs is dropped if HARQ-ACK(0) andHARQ-ACK(1) are DTX and HARQ-ACK(2) and HARQ-ACK(3) are NACK.
 5. Themethod according to claim 1, wherein the primary cell includes a primarycomponent carrier (PCC) and the secondary cell includes a secondarycomponent carrier (SCC).
 6. A communication apparatus configured totransmit uplink control information in a situation in which a pluralityof cells including a primary cell and a secondary cell is configured ina wireless communication system, the communication apparatus comprising:a radio frequency (RF) unit; and a processor, wherein the processor isconfigured to select one PUCCH resource corresponding to a plurality ofHARQ-ACKs (Hybrid Automatic Repeat reQuest-Acknowledgements) from aplurality of PUCCH resources for PUCCH (Physical Uplink Control Channel)format 1 and transmit bit values corresponding to the plurality ofHARQ-ACKs using the selected PUCCH resource, wherein the relationshipamong the plurality of HARQ-ACKs, PUCCH resource and bit values includesthe relationship of the following Table 1 TABLE 1 HARQ-ACK(0)HARQ-ACK(1) n⁽¹⁾ _(PUCCH, i) b(0)b(1) ACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 11NACK NACK/DTX n⁽¹⁾ _(PUCCH, 0) 00

where HARQ-ACK(0) indicates ACK/NACK/DTX response to a data blockrelated to the primary cell, HARQ-ACK(1) indicates ACK/NACK/DTX responseto a data block related to the secondary cell, n⁽¹⁾ _(PUCCH, i) (i=0, 1)indicates a plurality of PUCCH resources for the PUCCH format 1, n⁽¹⁾_(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH (PhysicalDownlink Control Channel) on the primary cell, and b(0)b(1) indicatesthe bit values.
 7. The communication apparatus according to claim 6,wherein the relationship among the plurality of HARQ-ACKs, PUCCHresource and bit values further includes the relationship of thefollowing Table 2 TABLE 2 HARQ- HARQ- HARQ- HARQ- ACK(0) ACK(1) ACK(2)ACK(3) n⁽¹⁾ _(PUCCH, i) b(0)b(1) ACK ACK NACK/DTX NACK/DTX n⁽¹⁾_(PUCCH, 0) 11 ACK NACK NACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 10 NACK ACKNACK/DTX NACK/DTX n⁽¹⁾ _(PUCCH, 0) 01 NACK NACK NACK/DTX NACK/DTX n⁽¹⁾_(PUCCH, 0) 00

where HARQ-ACK(0)(1) indicates ACK/NACK/DTX responses to data blocksrelated to the primary cell, HARQ-ACK(2)(3) indicates ACK/NACK/DTXresponses to data blocks related to the secondary cell, n⁽¹⁾ _(PUCCH, i)(i=0, 1, 2, 3) indicates a plurality of PUCCH resources for the PUCCHformat 1, n⁽¹⁾ _(PUCCH, 0) indicates a PUCCH resource linked to a PDCCH(Physical Downlink Control Channel) on the primary cell, and b(0)b(1)indicates the bit values.
 8. The communication apparatus according toclaim 6, wherein transmission of the plurality of HARQ-ACKs is droppedif HARQ-ACK(0) is DTX and HARQ-ACK(1) is NACK.
 9. The communicationapparatus according to claim 6, wherein transmission of the plurality ofHARQ-ACKs is dropped if HARQ-ACK(0) and HARQ-ACK (1) are DTX andHARQ-ACK(2) and HARQ-ACK(3) are NACK.
 10. The communication apparatusaccording to claim 6, wherein the primary cell includes a primarycomponent carrier (PCC) and the secondary cell includes a secondarycomponent carrier (SCC).
 11. A method for transmitting uplink controlinformation in a situation in which a plurality of cells including aprimary cell and a secondary cell is configured in a wirelesscommunication system, the method comprising: selecting one uplinkcontrol channel resource corresponding to a plurality of HARQ-ACKs(Hybrid Automatic Repeat reQuest-Acknowledgements) from a plurality ofuplink control channel resources; and transmitting modulation symbolscorresponding to the plurality of HARQ-ACKs using the selected uplinkcontrol channel resource, wherein a mapping relationship between theplurality of HARQ-ACKs and the modulation symbols is equal to a mappingresult of HARQ-ACKs and modulation symbols for one or more data blocksreceived on a single downlink carrier on the basis of one or more firstHARQ-ACKs for one or more data blocks related to the primary cell, ifone or more second HARQ-ACKs for one or more data blocks related to thesecondary cell, except the one or more first HARQ-ACKs, are all NACK orDTX (Discontinuous Transmission).
 12. The method according to claim 11,wherein transmission of the plurality of HARQ-ACKs is dropped if the oneor more first HARQ-ACKs are all DTX and the second HARQ-ACKs are allNACK.
 13. The method according to claim 11, wherein the primary cellincludes a PCC (Primary Component Carrier) and the secondary cellincludes a SCC (Secondary Component Carrier).
 14. The method accordingto claim 11, wherein the uplink control channel includes a PUCCH(Physical Uplink Control Channel) and the downlink control channelincludes a PDCCH (Physical Downlink Control Channel).
 15. Acommunication apparatus configured to transmit uplink controlinformation in a situation in which a plurality of cells including aprimary cell and a secondary cell is configured in a wirelesscommunication system, the communication apparatus comprising: an RF(Radio Frequency) unit; and a processor, wherein the processor isconfigured to select one uplink control channel resource correspondingto a plurality of HARQ-ACKs (Hybrid Automatic RepeatreQuest-Acknowledgements) from a plurality of uplink control channelresources, and transmit modulation symbols corresponding to theplurality of HARQ-ACKs using the selected uplink control channelresource, wherein a mapping relationship between the plurality ofHARQ-ACKs and the modulation symbols is equal to a mapping result ofHARQ-ACKs and modulation symbols for one or more data blocks received ona single downlink carrier on the basis of one or more first HARQ-ACKsfor one or more data blocks related to the primary cell, if one or moresecond HARQ-ACKs for one or more data blocks related to the secondarycell, except the one or more first HARQ-ACKs, are all NACK or DTX(Discontinuous Transmission).
 16. The communication apparatus accordingto claim 15, wherein transmission of the plurality of HARQ-ACKs isdropped if the one or more first HARQ-ACKs are all DTX and the secondHARQ-ACKs are all NACK.
 17. The communication apparatus according toclaim 15, wherein the primary cell includes a PCC (Primary ComponentCarrier) and the secondary cell includes a SCC (Secondary ComponentCarrier).
 18. The communication apparatus according to claim 15, whereinthe uplink control channel includes a PUCCH (Physical Uplink ControlChannel) and the downlink control channel includes a PDCCH (PhysicalDownlink Control Channel).